The present invention relates to printing presses and pertains particularly to a powder spray attachment for the delivery tray of a printing press.
Many small offset printing presses produce several hundred sheets per minute of printed copy which is stacked in a delivery tray as the sheets come out of the press. Some printing presses use a gravity feed delivery and others use a chain delivery feed for delivery of the sheets from the press to the delivery tray. The sheets, when they come from the press are usually still wet with ink and frequently the ink from one sheet will imprint the back of the next sheet. For this reason, spray attachments for spraying powder on the sheets as they are delivered into the tray are available for most machines. These attachments however usually comprises one or more open ended tubes that are directed into the delivery tray for blowing powder onto the sheets. Often times sheets which are printed have ink coverage only on certain areas. For this reason, it is frequently unnecessary to cover the entire sheet with powder.
Accordingly, it is desirable that some means be available for selectively delivering a spray powder to selected areas of printed sheets as they are ejected from a printing press.